Part of Auckland Airport's international arrival terminal is flooded after its sprinkler system was activated.

Fire shift manager Colin Underdown said around 30 fire crew had been called to the site just before 4pm.

Airport spokesman Simon Lambourne believed a construction worker might have accidently set the sprinklers off.

He said aside from minor damage to two of its screening machines the flooding had not been significant.

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Mr Lambourne said there might be a slight delay, but did not think it would cause a significant hold up in those going through customs.

He added there was also an earlier incident this afternoon that had led to the airport being evacuated from the departure lounge on the first floor.

"About 300 people were evacuated but went in again after half an hour."

Mr Lambourne said the evacuation hadn't caused any flight delays.

One traveller, Andrew Brown tweeted about being greeted by blaring alarms and dripping water upon his arrival.

"Alarms going off & water dripping from the roof onto x-ray machines in customs!!!

"Hope the ground staff got the covers on in time so hot spot still works when play resumes."

Jamie Newman tweeted his frustration.

A group of fans of the Australian pop-rock group, At Sunset, had been adding to the airport disruption in their attempts to catch a glimpse of the band that was due to arrive around the same time as the incidents unfolded.